Author Topic: Valhalla 2701c schematics + firmware V3  (Read 5271 times)

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Online lowimpedance

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Re: Valhalla 2701c schematics + firmware V3
« Reply #25 on: February 19, 2018, 10:51:53 pm »
 If Valhalla can supply the documentation for the LNF version that would make life so much easier and then this would be a very interesting project. A frustrating learning experience is good ! , it will stick in your mind and will be very useful for those 'other' frustrating learning occasions  :P.
The odd multimeter or 2 or 3 or 4...or........can't remember !.
 

Offline wictor

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Re: Valhalla 2701c schematics + firmware V3
« Reply #26 on: February 21, 2018, 06:33:53 am »
Hi!

Does anyone have full schematics for older 2701 or 2701B? I cannot even find pictures of the boards of the oldest model.

Wictor
« Last Edit: February 21, 2018, 06:47:48 am by wictor »
 

Offline jasonbrent

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Re: Valhalla 2701c schematics + firmware V3
« Reply #27 on: February 21, 2018, 04:42:31 pm »
Hi!

Does anyone have full schematics for older 2701 or 2701B? I cannot even find pictures of the boards of the oldest model.

Wictor

Check with http://artekmanuals.com/manuals/other-manuals/ -- he responded quickly when I asked if what he had on the 2701c contained the LNF variant (it did not). He lists the 2701A/B/C.
 

Offline wictor

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Re: Valhalla 2701c schematics + firmware V3
« Reply #28 on: February 22, 2018, 06:04:35 am »
Hi!

Does anyone have full schematics for older 2701 or 2701B? I cannot even find pictures of the boards of the oldest model.

Wictor

Check with http://artekmanuals.com/manuals/other-manuals/ -- he responded quickly when I asked if what he had on the 2701c contained the LNF variant (it did not). He lists the 2701A/B/C.

Yes, that seems to be best option right now.
 

Offline jasonbrent

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Re: Valhalla 2701c schematics + firmware V3
« Reply #29 on: February 27, 2018, 05:13:51 am »
Update on my -LNF saga:

* Valhalla Scientific does not appear to have the -LNF schematics
* Their VP of engineering reached out to me in lieu of the schematics, but I've yet to hear back from him after my initial response. :/
* I've sourced and replaced every single relay ($$) and TR6-12 in the "output drive" section.
* I've sourced and replaced every socketed IC except the microprocessor, NOVRAM, and ROM.
* I've verified that the digital portion of the board appears to be doing the right thing at the signal level, things just aren't making it out the analogue end properly.

I've at least partially convinced myself that the components missing on the board are appropriate for the LNF variant after much tracing of the schematics. Otherwise, I think the -LNF is nothing more than a smaller transformer in place of the 1200V one, removal of the HV circuitry on the board, a rom check or different rom, and the addition of some 0.01uF filter caps across the banana plugs, and a few other spots on the board. Where I lose the convincing is around the analogue output side.... the manual describes HV analog function and I simply don't have the clue at the moment to translate it into how this should work otherwise.

Symptoms are still the same, unfortunately.

I've got replacement electrolytics en route as a hail mary.

-j
 

Offline precaud

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Re: Valhalla 2701c schematics + firmware V3
« Reply #30 on: March 01, 2018, 06:57:17 pm »
I have a PDF op/service manual for the 2701C which Valhalla gave to me a few years back. It mentions the -LNF option but gives no circuit details. PM me if you can use it.
 

Online lowimpedance

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Re: Valhalla 2701c schematics + firmware V3
« Reply #31 on: March 01, 2018, 11:37:08 pm »
I have a PDF op/service manual for the 2701C which Valhalla gave to me a few years back. It mentions the -LNF option but gives no circuit details. PM me if you can use it.
The manual I have , and have attached here, also mentions this option but has no further detail  either :(.  What I find odd is that Valhalla themselves say they don't have the details.
Or some one couldn't be bothered hunting through a filing cabinet  :P
The odd multimeter or 2 or 3 or 4...or........can't remember !.
 

Offline precaud

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Re: Valhalla 2701c schematics + firmware V3
« Reply #32 on: March 02, 2018, 03:47:21 am »
At least you have the GPIB option. Would be interesting to see what happens on the display at power up if you remove the header ribbon connector before hand.

The manual I have says of the -LNF version that, if the GPIB option is installed, the noise improvement is reduced by 50% ....
 

Online lowimpedance

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Re: Valhalla 2701c schematics + firmware V3
« Reply #33 on: March 02, 2018, 03:52:43 am »
Same here in my manual !. As for the unit that Jason is working on its origin , as a LNF at least, is unclear as it certainly looks like some one had access to a proper LNF (as they have copied the firmware too) and have butchered a standard 2701c to become a LNF as you see in Jasons pictures above.
« Last Edit: March 02, 2018, 03:57:30 am by lowimpedance »
The odd multimeter or 2 or 3 or 4...or........can't remember !.
 

Offline jasonbrent

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Re: Valhalla 2701c schematics + firmware V3
« Reply #34 on: March 02, 2018, 04:12:35 am »
I have a PDF op/service manual for the 2701C which Valhalla gave to me a few years back. It mentions the -LNF option but gives no circuit details. PM me if you can use it.
The manual I have , and have attached here, also mentions this option but has no further detail  either :(.  What I find odd is that Valhalla themselves say they don't have the details.
Or some one couldn't be bothered hunting through a filing cabinet  :P

I'm beginning to think that the -LNF variants were hand adjusted, potentially by a very small number of people (1?); and those people/person isn't with them anymore, so the information is lost. Honestly, the only differences I see, other than removing a lot of the HV path is 7 capacitors. 4 across each of the pairs of terminals, and 3 in parallel with R42A/R42B/R41 -- 0.1uF 5% 100V caps that might be custom rolled (yellow, paper? unsure, can't take a picture at the moment).

Valhalla told me to check the output voltages and all of the rails match the schematic, except the HV rail between I and J on sheet 1 of the schematics.... that one simply isn't specified. I'm getting 376V potential across I/J which appears to simply match TR201's output between E20 and E21 (280V) plus TR202's E9-E10 (93V). I asked them to confirm what voltage should exist there and was told that they don't know --- they don't have an LNF to check. :)

As an aside, on sheet 1, TR6, part of the output drive, is listed as a TIP29A in the parts list; is a TIP31A a reasonable substitute there? I *THINK* it is based on the specs of each... but the TIP29A I pulled from the board seems to be fine according to this peak atlas DCA75.

I sat down with a "real" EE and the schematics a couple of days ago to look at the output drive section and at this point I'm wondering if the zener, D3, isn't misbehaving. In circuit, it is ~1.5MOhm in 1 direction, and ~55kOhm in the other... but in circuit could be lying to me.

Incidentally, I sent the same pictures from earlier in this thread to Valhalla asking if they could verify if that is what an LNF was supposed to look like, or if it was someone else's butcher job... They didn't appear to know, at least, they didn't answer that question, which was the only real question in my email. :)

Eventually this thing will work again....

-j
« Last Edit: March 02, 2018, 04:14:53 am by jasonbrent »
 

Offline Edwin G. Pettis

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Re: Valhalla 2701c schematics + firmware V3
« Reply #35 on: March 02, 2018, 05:03:37 am »
Valhalla was not known for using 'special' components, the vast majority of the components in their instruments were standard off-the-shelf even if they had in-house numbering on them.  During the period we were making all of their PWW resistors, I do not recall a LNF option in the 2701C models in production at the time.  This 'option' may have been a 'special' done for a particular customer at some time before the 'C' version and the instrument you have come by may have been somebody's attempt at bodging an LNF into the unit.  I have a 2701C manual from Valhalla and first chance I get, I'll take a look at it and see if there is anything in it about this option.
 

Offline jasonbrent

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Re: Valhalla 2701c schematics + firmware V3
« Reply #36 on: March 02, 2018, 05:08:13 am »
Valhalla was not known for using 'special' components, the vast majority of the components in their instruments were standard off-the-shelf even if they had in-house numbering on them.  During the period we were making all of their PWW resistors, I do not recall a LNF option in the 2701C models in production at the time.  This 'option' may have been a 'special' done for a particular customer at some time before the 'C' version and the instrument you have come by may have been somebody's attempt at bodging an LNF into the unit.  I have a 2701C manual from Valhalla and first chance I get, I'll take a look at it and see if there is anything in it about this option.

Hmmm, useful information. The serial# sticker on the outside says "2701C-LNF" for what it's worth. The only other reference I found to LNF (other than ebay scrapers), is an index of content in use at Sandia National Labs in the recent past. It lists both a 2701C and a 2701C-LNF in their possession. http://www.sandia.gov/psl/_assets/documents/Electrical%20Lab%20Supported%20Equip 21May2015.pdf
 

Offline precaud

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Re: Valhalla 2701c schematics + firmware V3
« Reply #37 on: March 02, 2018, 02:21:05 pm »
I have a couple 2701C's here in the repair pile, I'll look and see if either of them are LNF's.

Quote
The serial# sticker on the outside says "2701C-LNF" for what it's worth. The only other reference I found to LNF (other than ebay scrapers), is an index of content in use at Sandia National Labs in the recent past. It lists both a 2701C and a 2701C-LNF in their possession.

That makes sense. I tested that unit when it was offered for sale and decided to pass on it. You must have bought it on eBay from "solanotraders", an aggressive eBay flipper. I would advise you to assume that almost anything you buy from him has significant issues. I attend the same industrial auctions he does, and it is part of my job to make sure he doesn't get TE stuff that works  :)
 

Offline jasonbrent

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Re: Valhalla 2701c schematics + firmware V3
« Reply #38 on: March 02, 2018, 02:51:47 pm »
I have a couple 2701C's here in the repair pile, I'll look and see if either of them are LNF's.

Quote
The serial# sticker on the outside says "2701C-LNF" for what it's worth. The only other reference I found to LNF (other than ebay scrapers), is an index of content in use at Sandia National Labs in the recent past. It lists both a 2701C and a 2701C-LNF in their possession.

That makes sense. I tested that unit when it was offered for sale and decided to pass on it. You must have bought it on eBay from "solanotraders", an aggressive eBay flipper. I would advise you to assume that almost anything you buy from him has significant issues. I attend the same industrial auctions he does, and it is part of my job to make sure he doesn't get TE stuff that works  :)
I had to go back and look, no it wasn't "solanotraders". I'll add that info to my mental filing cabinet though. :)
 

Offline precaud

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Re: Valhalla 2701c schematics + firmware V3
« Reply #39 on: March 03, 2018, 03:07:35 pm »
Neither of my 2701C's are -LNF's...
 

Offline jasonbrent

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Re: Valhalla 2701c schematics + firmware V3
« Reply #40 on: March 03, 2018, 03:29:00 pm »
Neither of my 2701C's are -LNF's...
Trade you one Rare^WVintage^Unique -LNF for a working 2701C in your pile? :-)

I guess I'll start up a thread in the Repair section and see if we can crowd source this. :)

Thank you for checking.

-j

 

Offline precaud

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Re: Valhalla 2701c schematics + firmware V3
« Reply #41 on: March 03, 2018, 03:46:23 pm »
Trade you one Rare^WVintage^Unique -LNF for a working 2701C in your pile? :-)

Thanks for your kind offer  :)

Neither of mine are working, they've been patiently waiting in the repair pile for a couple years. I put numerous hours into troubleshooting each of them at some point with only partial success, and had to put them aside for a rainy day. Global Climate Change has given us far fewer such days, and so they have sat unattended to  ...   :)
 

Offline jasonbrent

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Re: Valhalla 2701c schematics + firmware V3
« Reply #42 on: March 10, 2018, 02:03:37 am »
TL;DR: To test the analog circuitry, I took the digital out of the equation (I think). Still have the voltage potential where it shouldn't be. As best I can tell, with no signal out of IC5 pin 10 to TR12, the high voltage should go to 0va through D7 (I think..).

After setting this aside for a few days, I pulled pins 1,2,12,13 off of IC112 (feeds the 2 variable duty cycle square waves into the precision resistor chain and on to the chopper amp before hitting the mosfet output chain) temporarily to take the digital bits out of the equation. I still have the voltage potential that shouldn't be there. For anyone playing the home game (OPs post, "main board cct.pdf"), on the main PCB diagram, sheet 1, the voltage I see across the outputs when in standby mode is the same voltage I see across the pair of diodes D6/D5 and across C12.

On sheet 3, power supply, R223 (high voltage output, near "J" on the right) is a piece of wire on mine. R224 is in place, however. I don't quite understand how the windings on the low voltage transformer between E9/E10 that feed through "L" back to sheet 1 between R7 and the slow blow fuse F1 works. It basically looks like the T201 transformer sends to I/J on the output side, but T202 also helpfully gives another 120V as "L".

I think need to study input "L" at the very top of sheet 1 to understand the relationship between that, the F1 fuse, D1/D2/D5/D6/D8/D9... if I pull the fuse F1, I still get the same voltage potentials on the outputs... but I think that's an "input" protection fuse vs. output. I don't grok the current flow in this thing.  :-//.

While thing thing works exactly as it did when I received it despite all of my cutting/removing/replacing/testing, I'd be hard pressed to even put it up for sell as it'd just feel slimy.

 |O |O |O |O |O

« Last Edit: March 10, 2018, 04:18:11 am by jasonbrent »
 


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